Field of the Disclosure
This disclosure relates to turbochargers having a rotatable shaft passing through a bearing housing between a turbine housing and a compressor housing. More particularly, this disclosure relates to a turbine-end bearing support with an extending support bar within the bearing housing.
Description of Related Art
Advantages of turbocharging include increased power output, lower fuel consumption and reduced pollutant emissions. The turbocharging of engines is no longer primarily seen from a high-power performance perspective, but is rather viewed as a means of reducing fuel consumption and environmental pollution on account of lower carbon dioxide (CO2) emissions. Currently, a primary reason for turbocharging is using exhaust gas energy to reduce fuel consumption and emissions. In turbocharged engines, combustion air is pre-compressed before being supplied to the engine. The engine aspirates the same volume of air-fuel mixture as a naturally aspirated engine, but due to the higher pressure, thus higher density, more air and fuel mass is supplied into a combustion chamber in a controlled manner. Consequently, more fuel can be burned, so that the engine's power output increases relative to the speed and swept volume.
In exhaust gas turbocharging, some of the exhaust gas energy, which would normally be wasted, is used to drive a turbine. The turbine includes a turbine wheel that is mounted on a shaft and is rotatably driven by exhaust gas flow. The turbocharger returns some of this normally wasted exhaust gas energy back into the engine, contributing to the engine's efficiency and saving fuel. A compressor, which is driven by the turbine, draws in filtered ambient air, compresses it, and then supplies it to the engine. The compressor includes a compressor impeller that is mounted on the same shaft so that rotation of the turbine wheel causes rotation of the compressor impeller.
Turbochargers typically include a turbine housing connected to the engine's exhaust manifold, a compressor housing connected to the engine's intake manifold, and a center bearing housing coupling the turbine and compressor housings together. The bearing housing encloses and supports the rotating shaft.
This disclosure focuses on bearing housing design. Bearing housings are typically cast with a hollow core forming a cavity that allows flowing oil to lubricate and cool the bearing housing and the rotating shaft. The general oil flow through the bearing should, whenever possible, be vertical from top to bottom. The lubricating oil flows into the turbocharger at a pressure of approximately four bar. As the oil drains off at low pressure, the oil drain pipe diameter must be larger than the oil inlet pipe. An obstruction in the oil drain pipe can result in drain cavity oil flooding and resultant back pressure in the bearing system.
The rotating shaft is typically support by cradles in the bearing housing. Journal bearings are stronger and can take more abuse than dual ball bearing. Typically, twin journal bearings are used, including one on the turbine end, which is the preferred bearing system in this disclosure. Oil is transported through a passageway to the journal bearing at the turbine end and through another passageway to another journal bearing closer to the compressor housing. Pressurized oil can be provided through an oil intake and through a passageway to the thrust bearing, and oil making its way toward the compressor can be blocked by an insert and a sealing system between the bearing housing and the compressor housing as shown in BorgWarner's U.S. Pat. No. 8,348,595, which is incorporated herein by reference. The lack of proper turbine end bearing support could cause shaft motion failures.
Existing top-supported cradle designs are shown in FIGS. 1 through 3 wherein the rotating shaft in a bearing system is engaged with a turbine-end support extending down from the top of the bearing housing cavity. There can be issues with stress in the cooling dam area with certain top-supported cradle designs. Cooling of the turbine-end bearing support is a primary concern with efficient bearing housing designs.
Introducing air dams and air cooling in addition to optimized oil cooling presents challenges in shaft motion prevention design and with journal bearing support cradle stiffness.
Thus, there is a need for a turbocharger with a modified turbine-end bearing support and improved cooling capabilities.